1. Field of the Invention
The present invention relates to a field sequential lighting device for emitting light corresponding to a plurality of colors sequentially, and an image projecting device having the lighting device.
The present application is based on a Japanese patent application filed with the Japanese Patent Office on Oct. 22, 2004 (Japanese Patent Application No. 2004-308273) and incorporates by reference its contents.
2. Description of Related Art
Recently, lighting devices for emitting light in a plurality of specific colors (wavelengths) have been proposed which have a light source for emitting white color light and a color wheel formed by disposing trimming (color) filters, through which light corresponding to specific wavelengths of colors, i.e., red (R), green (G), and blue (B) can be transmitted, on divided sections on a rotatable plate so that the light emitted from the light source corresponding to each color R, G, and B can be emitted sequentially by rotating the color filters. In general, single-plate field sequential image projecting devices (projectors) and endoscope devices use such lighting devices for emitting a plurality of colors sequentially.
In such single-plate field sequential image projecting devices, the light corresponding to each color, i.e., R, G, and B, is converted by spatial modulating elements, e.g., transmissive LCDs so that the modulated colors represent image information corresponding to R, G, and B during a lighting period, and each of R, G, and B is superimposed over time; thus, such a structure enables color display. In addition, single-plate field sequential image projecting devices use discharging lamps, i.e., ultra-high pressure mercury lamps, as light sources in the projectors because the discharging lights can form a point source of light with high emission intensity. With respect to spectrums, lights emitted from such ultra-high pressure mercury lamps has several characteristic bright lines which are unique to mercury. As shown in FIG. 11, many of the bright lines have peaks in the blue to ultra-violet region, and they do not exist in a red-color region. Therefore, as shown in FIG. 12, an intensity of the R-light (red-colored light) is weak in such conventional ultra-high pressure mercury lamps; thus, color reproducibility of the R-light is not sufficient. As a result of this, in order to realize adequate white balance, it is necessary to weaken intensities of the G and B lights relatively.
With respect to such characteristics of the light spectrum, UV cutting filters are disposed between a reflector for concentrating light emitted from the lamp and the spatial modulating element in order to protect human bodies and liquid crystals from damage caused by the UV light. Also, in order to prevent damage caused by heat, IR (Infrared Ray) filters are disposed. By doing this, visible white light can be emitted by cutting out light at wavelengths of 420 nm or less, and light at wavelengths of 720 nm or greater. The white light is transmitted through the color filters having filtering properties of R, G, and B colors shown in FIG. 11 and formed on the rotating color wheel. As a result of this structure, the field sequential lighting operation of the colors, i.e., R, G, and B is available as shown in FIG. 12.
On the other hand, lighting devices having wavelength converting elements have been proposed for adjusting color balances in lighting devices, e.g., ultra-high pressure mercury lamps used in projectors (see Japanese Unexamined Patent Application, First Publication No. 2002-90883). The lighting device used in projectors disclosed in this publication is used for improving color balance in order to supplement the red color by inserting wavelength converting elements for changing the wavelength of ultra-violet rays into the wavelength of visible light (in particular, red light) because light emitted light from the ultra-high pressure mercury light inevitably lacks in red color.